Heat Pump Desuperheater Calculator

A desuperheater is a small heat exchanger tapped into a geothermal heat pump's refrigerant loop that captures otherwise-wasted heat and pre-heats (or fully heats) your domestic hot water whenever the heat pump is running. This calculator first figures out how much energy your household actually needs for hot water: gallons per day times 8.33 (a gallon of water's weight in pounds) times the temperature rise from inlet to target, which gives BTU of heating demand. Separately, it computes what the desuperheater can supply — a percentage of the heat pump's total capacity (typically 5-15%) — and multiplies that rate by how many hours per day the heat pump actually runs, since a desuperheater only produces hot water while the compressor is active. Comparing daily desuperheater output against daily hot water need gives the "percent met" figure, capped at 100% since any surplus heat beyond your hot water demand isn't credited.

Annual savings convert the energy actually offset into the electric kilowatt-hours a standard water heater would have consumed to do the same job, accounting for that water heater's efficiency, then price it at your electricity rate. One quirk worth knowing: the "Annual Saved (kWh)" output is a straight BTU-to-kWh conversion of the offset energy and doesn't change with water heater efficiency (the efficiency term algebraically cancels in that calculation), while "Annual kWh Replaced" divides by efficiency to represent the actual purchased electricity a real water heater would have drawn — so don't expect those two closely-named numbers to match. The biggest sensitivity is run hours: a heat pump that only cycles a couple hours a day in shoulder seasons will offset far less hot water than one running most of the day during a cold snap.